The race to replace Ted Ken nedy in the US Senate has come down to one issue, and it’s not Sen. Kennedy’s “legacy.” It’s the misshapen health-care bills that have scared the bejesus out of an ever-growing majority of American voters, even in this bluest of states.

A month ago, he was 30 points behind his Democratic opponent — the don’t-make-no-waves attorney general, Martha Coakley. She was cruising, playing the one card she never leaves home without — the gender card.

Then the specifics of ObamaCare started leaking out. The cuts in Medicare — $500 billion, or as Brown prefers to say, “half a trillion dollars.” Then the state’s union members began to hear about the president’s insistence on a 40 percent tax on their “Cadillac” health-care plans.

Overnight, the old dichotomies — Democrat-Republican, red-blue — lost their resonance. This has become a struggle for self-preservation — medical and fiscal. As the old folk song goes, Which side are you on?

“This race affects everyone — everyone,” Brown says over and over again. “Forget about the letter after my name. If I win, this broken health-care bill goes back to the drawing board.”

Which is why the city was buzzing yesterday with unconfirmed reports that President Obama may have changed his mind about staying out of the race. The rumor was that he may fly into Boston this weekend on behalf of the flailing Coakley, whose lead in the latest poll is just two points.

Coakley is still favored to win, but what Brown calls “the machine” is stunned. In the most recent Rasmussen poll, he leads her among independents 71-23.

“They are in an absolute panic mode,” one prominent Bay State Democrat was saying yesterday. “They don’t care if bringing in Barack energizes the Republicans and independents — how much more energized can they get? Obama’s people have to get the minority vote out, and Coakley sure can’t do it herself. It’s risky, but it may be the only way now to save her.”

The national Democrats are pumping hundreds of thousands of dollars into the race in the final days. On TV and radio, Brown’s first name is now “Republican,” as in “Republican Scott Brown.”

The Service Employees International Union, moveon.org, NARAL — all the usual suspects are on board.

But Coakley’s first 30-second hit piece fell a bit flat when, at the end, her campaign misspelled the name of her state as “Massachusettes.” “Maybe Martha should talk to some people who actually live here,” Brown said yesterday.

The deluge of attack ads began Monday, a couple of hours after the last debate. Coakley had turned in yet another lackluster performance — informing the audience that there were no terrorists left in Afghanistan, two days after one of the slain CIA operatives was buried in nearby Bolton and on the same day that three US servicemen were killed in the nation that she seems to think is terror-free.

But Brown won the debate when he fielded a question from the hyperliberal moderator, David Gergen, who asked him how he could possibly vote to kill health care while sitting in Ted Kennedy’s seat. “With all due respect,” Brown told the chat-show fixture, “this is not Ted Kennedy’s seat. It is the people’s seat.”

Brown was in the midst of an Internet “money bomb” fund-raiser, and after slapping down Gergen, by night’s end he’d raised $1.3 million — $800,000 above the campaign’s goal.

In the state’s suburban town halls, voters are lining up to get absentee ballots, just in case the weather takes a turn for the worse Tuesday. In Yarmouth, out on Cape Cod, for example, 183 residents voted absentee in last month’s primary. By Tuesday, the number of absentee ballots given out there was 622. It’s the same in all of the more conservative cities and towns.

Despite the bitter January cold, the Brown campaign has been swamped with volunteers. On the weekends, Brown “standouts” can be seen at every major intersection.

Representing a heavily Democratic district in the state Senate, Brown is used to having his yard signs disappear, but this time there’s a difference. “My own supporters are stealing them from each other,” he said. “They say, I need it more than you. I live on a busier street.”

The Democratic establishment is relying on yesterday’s tactics. On Tuesday night, a Weekly Standard reporter was assaulted by a Democratic operative outside a Coakley fund-raiser in Washington. The video was quickly posted on the Internet — but the Boston Globe, the Kennedy family house organ, pretended it was still 1973. Its headline: “Reporter takes stumble.”

Just like Martha Coakley. She may yet hang on to win — but even if she does, one thing is certain. As Scott Brown said, it’s not Ted Kennedy’s seat anymore.